thumb|German masons repointing a wall in 1948.
Repointing is the process of renewing the pointing, which is the external part of mortar joints, in masonry construction. Over time, weathering and decay cause voids in the joints between masonry units, usually in bricks, allowing the undesirable entrance of water. Water entering through these voids can cause significant damage through frost weathering and from salt dissolution and deposition. Repointing is also called pointing, or pointing up, although these terms more properly refer to the finishing step in new construction. Tuckpointing is also commonly used as a synonym, though its formal definition is technically different.
History
Traditionally, mortar was made with lime and sand, producing lime putty. In the early 20th century, masons began using Portland cement, a strong, fast drying cement. Masonry cement made its appearance in the 1930s, which is a combination of Portland cement and ground limestone.
Repointing process
Examining the structure
Before starting any actual work, building owners examine the masonry units, mortar, and the techniques used in the original construction.
Establishing materials
thumb|Spalling
Examining the structure before working will also help establish the strength and permeability of the original mortar in order to match the new. It helps to establish what the original components of the old mortar are in order to find the best match. It is essential that the mortar used for repointing have similar performance characteristics to the original mortar used in a building.
thumb|Restoration (before and after) of a Georgian brick facade in [[Limerick, re-pointed in Irish Wigging, using hybrid lime mix mortar, after replacing damaged bricks with matching salvaged bricks]]
An architectural conservator can perform a mortar analysis in order to make recommendations for replacement mortar that is both physically and aesthetically compatible with the building. There are two common methods of analyzing mortar. The first is called "wet chemical" in which a sample of mortar is crushed and mixed with a dilute acid. The mortar will be broken down, and the type of mortar and sand used will be determined by color and texture. and in the middle of the joint. A hammer and chisel are then used for the rest of the mortar, closer to the masonry units.